Process of dewaxing



Oct. 11, 1966 3 Sheets- Sheet 2 Filed Aug.

.0 J28 wizmu 000 0N 000 0 0000 000* 000m 000m 000 000 00 00m 00m Inventor Patent Attorney Oct. 11, 1966 Filed Aug. 1, 1965 R. E. SPARKS PROCESS OF DEWAXING Sheets-Sheet 5 FIG-3 OIL YIELP INCREASEPBY WBLENDIHNG I I I I I I I I I I" FEED-SHOCK-CHILLED Z/l HEXANE/SOLVENT IOONEUTRAL BLENDING AND CENTRIFUGATION TEMPERATURE- -F.

CenIrifuguI Forge I380 6,5 8I6 G s I l I l I I I I I I I I 20 4O 6O 80 I00 I20 I I BLENDING TIME, SECONDS Potent AIIorney InvenIor I 200 zzo z io z eo.

3,278,4l3 Patented Oct. Ill, 1966 3,278,413 PROCESS OF DEWAXING Robert E. Sparks, Westfield, N..I., assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Aug. 1, 1963, Ser. No. 299,235 ll Claim. (Cl. 208-33) This invention relates to a process of dewaxing waxy oil fractions. The invention relates to a method of separating wax particles from a wax oil slurry by centrifugation. The invention relates to a method of increasing the degree of compaction of the wax cake formed in the peripheral area of the centrifuge whereby increased oil yields from the wax oil slurry and a decrease in oil content of the recovered wax can be efficiently obtained. Particularly, the present invention relates to a method of increasing the oil yield of the wax oil slurry and decreasing the oil content of the wax recovered from the centrifuge by breaking up the wax particles in the wax oil slurry by intensive agitation prior to feeding the Wax oil slurry to centrifugation. The wax particles in the slurry are broken up to form smaller particles of decreased aspect ratio which smaller particles form a more dense and more compact wax cake with less oil in the cake.

In conventional dewaxing processes, in order to get an efficient separation of wax from a wax oil slurry, it is necessary that the wax crystals be relatively large and that a large volume of solvent be added to the oil to get eflicient separation of the oil and solvent from the wax crystals. The high solvent to oil ratio is necessary to dissolve the oil trapped between the loosely packed large wax crystals. In filtration additional solvent is frequently added to wash out any remaining oil in the loosely packed wax cake on the filter. Small crystals cannot efiiciently be separated by filtration because the smaller crystals enter the filter cloth and quickly blind the filter thereby stopping the filtration.

Centrifugation has been an efiicient means for separating wax from waxy oil feeds. However, in order to get practical clarification rates in the centrifuge it is necessary to form relatively large w-ax crystals. Because of the relative small density between the wax crystals and the waxy oil slurry, the separation rate, particularly with small crystals, is very slow. In wax oil slurry separations by centrifu-gation, the clarification rate is a critical practical feature of the centrifugation operation. It has been found, however, that when large crystals are formed during the dewaxing operation, in order to obtain rapid clarification rates, that the large crystals which separated easily from the wax oil slurry in the centrifuge packed very loosely giving a wax cake in the centrifuge having a high porosity and high oil content. This decreases the oil yield from the wax oil slurry and also results in obtaining a wax from the centrifuge which has a high oil content. In using a centrifuge to separate wax particles from wax oil slurries, the oil yield and the concentration of oil in the wax separated was determined by the degree to which the wax could be compacted in centrifuge. It was found that high centrifugal forces must be applied to approach a high oil yield.

Slow chilled parafiinic stocks during dewaxing form crystals shaped like needles 2-5 1. wide and -100/1. long or plates -1000I-L wide depending on how the dewaxing step is carried out. Because of the high aspect ratio of this material, i.e. the ratio of length to thickness or width, the particles packed very loosely giving a cake having a high porosity and hence high oil content. The present invention is directed to a simple efficient method of reducing the aspect ratio of this material in a controlled manner whereby the aspect ratio of the crystalline material can be greatly reduced and the material can be made to pack much more closely under a given centrifugal force, thus forming a wax cake with less oil and obtaining a higher oil yield.

In accordance with .the present invention, a wax oil slurry obtained from a dewaxing process having wax particles with high aspect ratios is treated to break up the wax particles into particles which have substantially smaller particle size and greatly reduced aspect ratios. In one embodiment of the invention a wax oil slurry obtained by slow chilling a parafiinic feed, containing wax particles of a size in the range of 10 to 1000 at the largest dimension, is subjected to intensive agitation and the particles are broken to a size where the largest dimension is about 540 The thus treated wax oil slurry is then fed to a centrifuge and the crystalline material is separated by centrifugation from the oil slurry.

Waxy oil fractions or whole crudes can be dewaxed in a conventional manner to form a wax precipitate which can be treated. Crude oils, parafiinic crudes, naphthenic crudes, containing paraffinic waxes, crystalline or micro crystalline waxes, can be treated in accordance with the present invention.

The waxy oil feed being dewaxed can contain suitable diluents or solvents and/0r dewaxing aids. Normally, parafiinic or microcrystalline fractions having a high concentration of wax will be blended with a light naphtha or light paraffinic or aromatic solvent to aid in the process by decreasing the viscosity of the waxy oil feed, and/or to aid in the filtration or centrifugation step. The use of diluents or solvents in dewaxing are well known and will not be discussed in detail. Any dewaxing process can be used which results in obtaining wax crystals which can be separated by centrifugation. The two most well known commercial dewaxing processes are propane dewaxing which is carried out to a temperature of about -30 F. and MEK/toluene dewaxing which is carried out to a temperature about 0 F.

Applicants invention results in obtaining several process advantages. The slow chilled dewaxing techniques which are now in commercial use, such as MEK/toluene and propane dewaxing, form relatively large wax particles with high aspect ratios. The particle size and aspect ratio of the wax particles obtained by dewaxing can be reduced by feeding the wax oil slurry to a suitable device adapted to provide a high agitation and intensive mixing wherein the particles are broken. By controlling the period of time and intensity of the agitation the average crystal size and shape most desirable for a particular feed to obtain the best separation and compaction under particular operating conditions can be obtained. In this manner, high oil yield and low oil content wax is produced.

FIGURE 1 of the drawings shows the relative compaction efliciency of untreated wax oil slurries as compared with several wax oil slurries treated in accordance with the present invention.

FIGURE 2 of the drawings shows the effect of blending time and centrifuged force on the oil yield and oil content of the wax cake.

FIGURE 3 of the drawings illustrates the effect on oil yield of blending time and centrifugal force.

Whole crudes as well as fractions can be treated in a conventional dewaxing process to obtain a wax oil slurry which can be treated in accordance with the present invention. Paraffinic wax fractions boiling in a range of 300 F. to 1000 F. and containing 595% wax can be treated. An example of such paraflinic fractions is Solvent neutral, which has the following characteristics.

3 Solvent 100 neutral:

API gravity 34.6

Pour point, F. 90

Cloud point, F. 95 Distillation at mm. Hg:

IBP, F. 280

Density of DWO at 40 F. 0.902

Density of wax at -40 F 0.935

Percent wax removed, wt.

Pour point DWO, F

Cloud point DWO, F.

The crystalline Wax structure resulting from a specific dewaxing operation will depend on the particular dewaxing operation and the particular feedstock treated. For example, paraflinic stock such as Solvent 100 neutral when slow chilled will form needles from 10 to 100/L long or plates 20 to 1000 wide. Wax oil slurries containing microcryst-alline waxes obtained from dewaxing Bright stock by slow chilling will produce long crystal aggregates 2-4n by 5-50a in size. The above waxes as well as any other waxes which can be broken into smaller wax particles and the aspect ratio of the particles reduced can ladvantageously be treated in accordance with the present invention.

Breaking up the wax crystals in the wax oil slurry can be carried out by any type of apparatus which can cause a rapid and intensive agitation and break up of the larger crystals to smaller crystals in a controlled reproducible manner. Reproducible results have been obtained with specific feeds by using a Waring blender which can be operated between 50 r.p.m. and 18,000 r.p.m. Also, conventional homogenizers or mixers can be used. Any means by which the wax particles in the wax oil slurry can be treated to breakup the wax crystals in a controlled manner can be used. The particular method of breaking the wax crystals up does not form a critical part of the present invention. It is only necessary that the wax particles in the wax oil slurry be broken up in a controlled manner. Applicant has found, however, that it takes rapid and intensive agitation to break up the wax particles. Simple mixing or passage of the slurry through gear pumps or pumping devices does not result in a significant breakup of the wax particles or result in a substantial change in the aspect ratio of the particles. Applicant has found, particularly with using the Waring blender device, which is a commercially available equipment, that specific r.p.m. energy inputs and mixing times are critical in obtaining maximum compaction of the Wax crystals and still obtaining suitable clarification rates in the clarfication zone of the centrifuge.

The advantage in compaction gained in breaking the Wax crystals is due to changing the aspect ratio of the crystals not merely due to making the crystals smaller. For example, tooth picks dumped into a container, having a specified length to diameter ratio, i.e. aspect ratio, will pack and form a loose network of tooth picks. This network will have a certain void/ solid ratio. If you now take pretzel sticks which are about twenty times larger than the tooth picks, but having the same length to dilameter ratio as the tooth picks, i.e. aspect ratio, and dump them into a suitable container, they will pack and form a loose network which will have a void/ solid ratio which will be the same as the tooth pick void/ solid ratio. Solids of the same aspect ratio pack to the same porosity regardless of physical size. Another example, a box full of large marbles or small B-Bs will have the same fraction voids even though the particles in one case are much smaller.

On the other hand if the aspect ratio of the solids is changed, for example breaking up the pretzel sticks into four or five pieces and the broken pieces are put into a suitable container, the increased compaction obtained is substantial.

This is what applicants blender does to the wax particles. In breaking up needle or plate crystals, or crystal aggregates applicant changes the aspect ratio of the particles so that on centrifugation the crystals pack more closely, filling more voids and form a more compacted wax cake which contains less oil.

Where very large crystals are involved an increase in the clarification rate of the liquid can be realized because the broken wax particles have less drag per unit mass than the larger particle from which they were broken and will tend to settle faster, and to some extent will compensate for the lower settling velocity effect due to their reduced size.

In accordance with the present invention, waxy oil feeds can be dewaxed in conventional dewaxing operations'to obtain wax crystals which can be relatively easily separated in a centrifuge and which crystals can be broken up to reduce the crystal aspect ratio. This invention is not to be limited by the particular method of obtaining the wax crystals which are to be centrifuged. Normally the breaking up of the wax crystals, or blending to break up the wax crystals, and the centrifugation step will be carried out at about the same temperature as the dewaxing operation. For example with propane dewaxing the temperatures may be as low as 20 to -35 F. and MEK/ toluene dewaxing the temperatures may be in the range of 10 to +10 F. The particular dewaxing temperature is not critical to this invention and can be altered and varied with the pour point and feeds being treated. For example, in deoiling the temperatures will be higher. The gravitational field applied by the centrifuge to separate the wax particles from the Wax oil slurry will vary with the particular feed, the wax content of the feed, the particle size, the oil yield and oil content of the wax desired. The centrifuges can be operated at to about 15,000 Gs.

Applicants invention is directed to the improvement in centrifuging obtained by breaking up the wax particles in the wax oil slurry in such a manner that the aspect ratio of the particle is substantially reduced prior to feeding the slurry to the centrifuge. In this manner better wax compaction can be obtained, resulting in higher yields of oil and lower oil content of the recovered wax at the same gravitational force.

Any centrifuges which are conventionally used for separating wax particles from wax oil slurries can be used in accordance with the present invention, for example, disc stack centrifuges as well as other known types.

In a preferred embodiment of the present invention, a parafiinic waxy oil feed boiling in the range of 300 to 1000 F. and having 12-15 wt. percent wax is dewaxed in a conventional propane dewaxing process whereby it is chilled from about F. at a rate of 210 F. per minute to about 20 F. During the chilling, the wax precipitates in the form of long needle crystals ofon the average of 25,u. thick by 20-40a long. The Wax oil slurry is removed from the propane chiller at about 20 F. and is fed to a Waring Blendor operated at 15000-18000 r.p.m. and is subjected to the intensive agitating and breaking action of the blender for from 1040 seconds whereby the wax crystals are broken up into particles of about 25 x 5-20 which greatly reduces the aspect ratio of the particles.

The slurry is then fed to a conventional disc stack centrifuge. The slurry is centrifuged and a 75-85% oil yield is recovered and wax removed from the centrifuge has an oil content of between 15 and 30 wt. percent.

The invention may be better understood by reference to the accompanying examples.

Example 1 A paraffinic lubricating oil stock, Solvent 100 Neutral, was divided into four equal samples and placed in solution in approximately 2 volumes of hexane. The four samples were then cooled from approximately 120 F. to approximately 20 F. Wax precipitated out of solution in the form of needles 1-5n x 20-60a long. The wax oil slurries obtained from the chilling step were placed in the centrifuge machine operated at a temperature of 20 F. The level of the Wax in each of the centrifuge tubes was read as a function of time of cen-' trifugation until equilibrium level was reached. The separation of the wax was carried out in the centrifuge at various gravitational fields as follows: At 210 GS, 460 Gs, 860 Gs, and 1380 GS.

The first of the four samples was treated in the above manner. The remaining three samples prior to the centrifugation step were placed in a Waring blender and the wax crystals were broken up by blending at approximately 16,000 r.p.m. and at to F. The second sample was blended 8 seconds, the third sample for seconds, and the fourth sample for 180 seconds. After thus treating the wax oil slurries, samples 2-4 were centrifuged at 210 GS, at 460 GS, at 816 Gs, and 1380 GS. Microscopic examination of the blended samples showed that a large percentage of the wax particles had been broken up so that their aspect ratio was now much smaller.

FIGURE 1 shows the required centrifugation time at different centrifugal forces to reach a certain wax level in the centrifuge tube of a sample which was not blended, as compared with three samples that were blended, respectively, at 8 seconds, 30 seconds, and 180 seconds. It will be observed that as the time in the blender increases, the rate at which the wax moves to a given level in the tube increases. The data clearly show that breaking up the wax crystals reduces the aspect ratio of the crystallized material and thereby allows for faster and better compaction of the Wax crystals in the centrifuge tube. The data also illustrate that the higher gravitational force applied to the wax oil slurry results in a better compaction of the wax crystals than obtained at the lower gravitational force. The data clearly show the unexpected improvement in compaction obtained by blending. For example, for 30 seconds blending and centrifuging at 210 Gs for 60 minutes a wax level of about results. This is compared with a non-blended slurry which required 240 minutes of centrifuge time at 860 GS to reach the same wax level.

To show the effect of the improved compaction obtained in accordance with this invention on the oil content of the wax recovered, the oil contents of the wax layers were calculated and plotted against centrifugal force. These data are illustrated in FIGURE 2 of the drawings. The data clearly demonstrate the effect of blending the wax oil slurries prior to centrifuging an oil yield and oil content in wax. With reference to FIGURE 2 of the drawing, blending the wax oil slurry for about 30 seconds in a Waring blender and centrifuging at about 3000 Gs, results in recovering wax containing about oil and an oil yield of about 70%. To obtain comparable yields of oil and oil content in wax where no blending was carried out, it was necessary to operate at a gravitational force of about 12,000 Gs. This shows a significant improvement in the compaction efficiency resulting from breaking up the wax particles prior to carrying out the centrifugation step.

FIGURE 3 of the drawings is a plot of the data, from the same four samples, showing the effect of blending time on the yield of dewaxed oil. These data show that the most rapid improvement of blending or breaking up of the wax crystals is obtained with this particular apparatus in about the first 20-40 seconds. It is to be recalled that though breaking up the crystals into smaller particles with smaller aspect ratios allows greater compaction and higher oil yields, if the crystals are broken up into particles that are extremely small, the clarifica tion rate of these small crystals in the clarification zone of the centrifuge becomes slow. This effect operates against the efliciency obtained by the more compact wax particles. Therefore, there is an optimum between crystal size obtained for minimum aspect ratio for efficient compaction and crystal size which is so small that it prevents efficient clarification in the centrifuge.

The above data would have less significance if the wax particles generated during the breaking up of the wax crystals were so fine as to make it diificult to obtain clarified oil in the centrifuge. It was noted that at the lower blending times, where the major percentage of beneficial effect is obtained, the fine particles had no appreciable effect on the clarity of the liquid. However, at the high blending times used to plot the curves over a wide range, there did occur a strong effect of the fines on clarification. Although a wax level could be observed and plotted, the liquid above this wax contained very fine crystals and would have had a high cloud point. From FIGURE 3 of the drawings it is seen that the major beneficial effect is obtained within about the first 20 seconds or so of blending time, and in order to have clarification proceed as rapidly as possible it is preferred to blend for about 20-40 seconds with this particular blending apparatus.

Any controlled method of breaking up the wax crystals formed by the dewaxing operation can be used in accordance with the present invention as long as the means of breaking up the crystals can be controlled so that the desired crystal breakage can be obtained with each particular wax slurry and centrifugation operation to be carried out. Waring blenders, homogenizers, or any device capable of placing high shear forces on the crystals can be used. The aspect ratio of the wax particles formed by conventional slow chill processes is large. The wax particles on 'centrifugation packed very loosely forming a cake having a high porosity and hence a high oil content. The present invention, as above illustrated, shows a method of obtaining a substantial reduction in the aspect ratio of the crystals by breaking up the crystals into smaller particles having smaller aspect ratios under controlled conditions. The particles, however, are not broken up into sizes so small that clarification becomes a problem. Improved oil yield results at lower gravitational fields and wax cakes having substantially less oil content are obtained. This technique can also be used for deoiling wax.

The invention includes and covers breaking up of any crystals in any crystal-liquid slurry in order to make the aspect ratios of the crystal smaller, and to obtain better compaction of the crystals in the centrifugation operation. This would include methods of making various pure chemicals by crystallizing the chemicals from solution, such as xylene, which is crystallized from solution and later separated from its solute by centrifugation.

The invention is not to be limited by any particular theory of operation but only by the scope of the appended claim.

I claim:

A process for improving the separation of wax crystal particles from a wax-oil slurry obtained from dewaxing a paraffinic lubricating oil stock boiling in the range of 300-1000 F. and improving the compaction efficiency of the centrifuge used to separate the wax-oil slurry which comprises blending the wax-oil slurry at a speed of at least about 15,000 rpm. for a period of at least 10 seconds whereby the wax crystals are broken into smaller particles thereby substantially reducing their aspect ratio and passing the thus treated wax-oil slurry to a centrifuge 7 8 zone wherein the wax particles are separated from the 2,725,338 11/1955 Perry 20833 wax-0i1 slurry. 2,903,411 9/ 1959 Shuman 208-33 3,086,717 4/1963 Vroom et a1 24124 References Cited by the Examiner 2 03 9 4/1936 Jones 2Q8 33 ALPHONSO D. SULLIVAN, Examiner.

2,354 10/1938 Knowles et a1 208- H. LEVINE, P. E. KONOPKA, Assistant Examiners. 

